For some 15 years, feminist punk rocker Kathleen Hanna carried the torch of a movement seemingly defined by her furious investment in the cause and the artistry that brought it to national attention. As the energetic frontwoman for Bikini Kill throughout the nineties, followed by the hugely popular dance group Le Tigre, Hanna was an unstoppable presence both onstage and off. Her impact is effectively explored in Sini Anderson’s documentary portrait “The Punk Singer,” which relies on interviews and robust footage from over the years to create an involving look at Hanna’s determination — as well as the forces that nearly toppled it.

Realized mainly with a grungy lo-fi video aesthetic, “The Punk Singer” begins with the early stirrings of Hanna’s artistry in the Olympia, Washington music scene in the late 1980’s, moving swiftly along with her snazzy rhythms and angry vocals as its built-in soundtrack. Chief interviewee Hanna provides plenty of insight into her own drive, particularly the mentality about female suppression in the music that led her to create the influential riot grrrl movement, while supporting voices put that inspiration in historical context.

Scholars and friends explain Hanna’s influence on the scene, connecting the dots between her aggressive efforts to counteract female abuse at rock concerts (urging all women to move to the front) with the likes of Rebecca Walker’s instigation of “third wave feminism” around the same time. Edited in a frenzied mashup of concert fragments and off-stage exchanges, “The Punk Singer” generally overcomes its rough production values by realizing the energy of Hanna’s achievements in terms of her passion and physical prowess.

Through it all, the movie endeavors to answer a question that the filmmaker smartly establishes upfront: In 2005, Hanna ended her stage career using the excuse that she had nothing left to say, but there was more to the story that nobody figured out until much later. The abrupt decision turned out to be a way of hiding a mysterious physical ailment only recently diagnosed as late stage lyme disease, the first real hindrance that no progressive attitude could fully overcome. Later scenes that find Hanna and her supportive husband (The Beastie Boys’ Adam Horovitz) contending with her growing frailty balance off the harsher bits with an emotional intimacy not immediately evident in her music.

Before it gets there, however, “The Punk Singer” mainly celebrates Hanna’s enthusiasm through those closest to her in early days, with fellow hard rocking female performers like Joan Jett and Kim Gordon weighing in. Though ostensibly hagiographic, their testimonies allow “The Punk Singer” to investigate Hanna’s symbolic power without sacrificing her personal connection to the cause; more than your average MTV-ready overview, “The Punk Singer” is essentially a documentary about activism. Without Hanna’s commitment, one cohort suggests, “we all would’ve starved to death culturally.” Even those who know her treat her like an icon.

Shifting rather abruptly to Hanna’s personal issues in its final third, “The Punk Singer” turns into a rushed survival story emboldened by the participation of those who support her now, including her husband. These scenes may not entirely gel with the earlier segments of the movie, but they’re nonetheless powerful for managing to capture Hanna’s frustrations over being unable to continue her mission with the same vitality that brought her success in the first place. Anderson compensates for an uneven pace with ample footage that speaks for itself. Culminating with a performance by Hanna’s new musical venture Julie Ruin, “The Punk Singer” demonstrates that neither Hanna’s cause nor her musical ambition have started to wane.

Criticwire grade: B+

HOW WILL IT PLAY? A definite crowdpleaser for fans of Hanna’s music, the movie should generate decent response in limited release and holds plenty of potential on VOD, where it’s likely to be embraced by its built-in audience.